The present invention relates to portable hardness testers, and in the particular a hardness tester having electro-optical mechanical encoding means and electronic decoding means responsive to and adapted for determining the hardness of a specimen.
A machine for testing the hardness of a specimen, such as a metal or plastic, is shown and described in U.S. Pat. No. 3,128,621--R. C. Scott, issued Apr. 14, 1964. Such a hardness testing machine utilizes the indentation method for testing the hardness of the specimen, which comprises the forming of an indentation on the specimen by a penetrator of specified shape and material, to which a thrust or a load of predetermined magnitude is applied. The resulting depth of penetration in the specimen is a function of the hardness of the specimen and is measured by means of a hardness number on a particular hardness scale, for example, the normal Rockwell scales being designated B and C. The smaller the depth of penetration the harder the specimen hardness and consequently the larger the numerical value of the hardness number.
In particular, the indentation method requires first the application of a minor load by the penetrator to the specimen, to thereby establish a reference point that minimizes inaccuracies due to surface imperfections in the specimen. Thereafter, a major load is applied to the specimen through the penetrator, thereby enlarging the depth of indentation penetration. The resulting depth of penetration is related to and determinative of the hardness of the specimen. Specifically, the resulting depth of penetration is the linear dimension along the indentation from the point of major loading (the point of maximum penetration) to a point spaced therefrom in the indentation and indicative of the indentation due to the minor load.
The selection of a specific hardness scale depends upon the kind of material to be tested, its previous history with respect to forming, hot and cold working and heat treatment and also its thickness. Each hardness scale requires the use of a specific penetrator and the application of predetermined minor and major loads. The most commonly used normal hardness scales are the Rockwell C and B scales. In particular, the Rockwell C scale is generally used for testing hardened and tempered steels. Its range is from a lower limit of C 20 upwards to about C 70 which is approximately the highest value for hardened steels.
In U.S. Pat. No. 3,486,373, to R. C. Scott, issued Dec. 30, 1969, a variable range load measuring assembly is described for utilization with a hardness tester having a hairpin load spring and of the type described in the aforementioned patent. A load equalizing beam lever is hingedly mounted to the hairpin load spring and by actuation of a hand lever it functions as a load divider thereby extending the number and scope of hardness scales for which the tester may be used. Thus, a hardness tester incorporating this variable range load measuring assembly can test specimens on both the normal and superficial hardness scales without the need of adding, substracting or substituting any part, component or device to the tester either prior to or during the making of the hardness tester.
While the hardness testers described in the heretofore mentioned patents have been used successfully for many years, they nevertheless have some disadvantages. These prior art hardness testers measured or sensed the linear displacement of the penetrator, which is determinative of the hardness number, by means of planetary gears and a rotatable graduated dial system. However, graduated dials and gears can only be made to specific tolerances. In the case of gears, this tolerance deteriorates with the increasing number of gears. Thus, some inaccuracy will result and will be further increased by the wearing down of these elements over years of usage. Also, in reading the hardness scale from the rotatably graduated dial the operator has had to interpret numbers between the graduation points. Thus, the hardness readings from these machines are only accurate to one point.
An object of the present invention is to overcome the inherent disadvantages of the prior hardness testers by incorporating electro-optical mechanical encoding means and electronic decoding means with an optical numerical display in lieu of the gearing and dial system utilized by the prior art. The optical electronic system of the present invention provides a reading more accurate than that which could be provided by the prior art, i.e., a reading accurate to one-half a point on the hardness number scale. Furthermore, the accuracy of the present invention will not deteriorate with usage as do the prior art machines, since it is an electronic means and not a mechanical means which senses the depth of penetration which is determinative of the hardness number. As the electronically determined hardness number is numerically displayed to onehalf a point of the hardness number, the operator need not make a transposition judgment as he did with the prior art devices utilizing a graduated dial.
These and other advantages of the present invention will become more apparent from the subsequent description of the present invention.